1. Field of Invention
The present invention is directed to a circuit for separating one type signal component, such as pulses, from another type signal component, such as a slowly reciprocating component, and more particularly to such a circuit for separating components where the respective frequencies of the signal components are about the same.
2. Description of the Prior Art
The use of continuous wave (Doppler shift) radar to measure heart rate of a patient is known. It works on the principle that a beating heart moves and of course a continuous wave radar can detect the presence of motion and its speed. Unfortunately, lung motion caused by breathing and patient movement is also detected by the radar. Further, the periodicity of the heart beat and breathing motions are similar which precludes separating signal components by a frequency filter.
One prior art structure for separating the two signals is as illustrated in U.S. patent application Ser. No. 527,768 filed Aug. 30, 1983 by M. Nowogrodzski and the instant applicant, now U.S. Pat. No. 4,513,748. That structure utilizes two radar frequencies and compares signals corresponding to the return signal at the two frequencies for producing a signal corrresponding to heart rate. Such a circuit, while effective, is relatively costly.